Scanning type charged particle beam microscope

ABSTRACT

To correct delay time of an electronic circuit of a scanning type charged particle beam microscope, in a scanning type charged particle beam microscope using electron beam, when a scanned image is sampled to a storing apparatus in synchronism with a scanning signal, the scanned image is sampled after correcting delay of an electronic circuit by a shift register having a variable stage number.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of sampling a scannedimage to a storing apparatus in a scanning type charged particle beammicroscope such as a scanning electron microscope or a scanning ionmicroscope.

[0003] 2. Description of the Related Art

[0004] In a scanning type charged particle beam microscope such as ascanning electron microscope or a scanning ion microscope, a secondaryelectron signal provided from a sample by a scanning signal is sampledto a storing apparatus in synchronism with the scanning signal tothereby constitute image data.

[0005] However, there is a delay of signal in an electronic circuit andtherefore, a scanning position of a charged particle beam and a storingposition thereof to a storing apparatus are shifted from each other byan amount of delay time of the electronic circuit. Further, whenscanning speed is changed, there poses a problem that at fast scanningspeed, a storing position of a storing image is delayed in comparison ofthat at slow scanning speed and a positional shift is produced in imagedata. Because according to the related art technology, start of scanningand start of storing an image are carried out simultaneously with eachother and therefore, the scanning position and the storing position areshifted from each other by an amount of delay time of the electroniccircuit. Further, the delay time of the electronic circuit is providedwith a dispersion produced by a characteristic of an apparatus andtherefore, the delay time cannot be corrected uniquely.

SUMMARY OF THE INVENTION

[0006] In order to resolve the above-described problem, according to anaspect of the invention, when a timing signal such as a start signal ofscanning is utilized as an image recording control signal, by delayingthe signal by an amount of delay of an electronic circuit by using ashift register having a variable stage number, the delay of theelectronic circuit is corrected to thereby prevent a positional shift ofan image.

[0007] According to a scanning type charged particle beam microscopeconstituted as described above, a storing position is shifted from ascanning position by the amount of a delay time period of the electroniccircuit and therefore, an operational position and the storing positioncoincide with each other. Further, when a stage number of the shiftregister having the variable stage number is adjusted while observingthe image, delay time inherent to an apparatus can simply be adjusted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a simple constitution view of a scanning type chargedparticle beam microscope;

[0009]FIG. 2 is a signal timing chart showing operation of FIG. 1;

[0010]FIG. 3 is a signal timing chart in adjusting an electroniccircuit; and

[0011]FIG. 4 is a constitution diagram of a shift register having avariable stage number defined by the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An explanation will be given of embodiments of the invention inreference to the drawings as follows.

[0013]FIG. 1 shows a simple constitution example of a scanning typecharged particle beam microscope according to the invention. Anexplanation will be given of operation thereof in reference to a signaltiming chart of FIG. 2.

[0014] A scanning signal generator 1 produces a start pulse 12 based ona referenced clock 11, generates a scanning signal 13 with the pulse asa reference, amplifies the signal by a magnitude necessary for adeflection amplifier 2, deflects a charged particle beam 4 by adeflector 3 and scans a surface of a sample 5. Secondary electron 6having an amount in accordance with a shape or properties thereof isgenerated from the surface of the sample 5 and therefore, the secondaryelectron 6 is detected by a secondary electron detector 7 to therebyprovide a secondary electron signal 14. As is apparent from FIG. 2, thesecondary electron signal 14 is delayed from the scanning signal 13owing to delay of an electronic circuit thereof.

[0015] The start pulse 12 produced by the scanning signal generator 1 isdelayed based on the reference clock 11 by a stage number designated bya stage number switching switch 9 by a variable stage number shiftregister 8 and supplied to a storage start input of an image storingapparatus 10.

[0016] The image storing apparatus 10 generates a write signal 16according to the invention when the image storing apparatus 10 isprovided with a storage start signal which is delayed based on thereference clock 11 by the stage number designated by the stage numberswitching switch 9 by the variable stage number shift register 8 andstores the secondary electron signal 14 based thereon at a storingapparatus at inside thereof. The stored data is displayed by a displayapparatus or utilized in image processing by a computer.

[0017] According to the related art apparatus, the secondary electronsignal 14 is stored at a storing apparatus at inside thereof based on awrite signal 15 of the related art apparatus.

[0018] When the apparatus according to the invention is compared withthe conventional apparatus, it is the feature of the invention that withregard to data stored to the storing apparatus, data at start time pointof the scanning signal 13 and data at storage start point, substantiallycoincide with each other. Further, the delay time of the electroniccircuit shows a characteristic inherent to the apparatus and therefore,when the delay time is corrected, the delay time can simply be correctedby switching the stage number of the variable stage number shiftregister 8.

[0019]FIG. 3 shows a method of adjusting correction of delay time of anelectronic circuit according to the invention. Scanning signals 19 and20, secondary electron signals 21 and 22 and write signals 23 and 24 inthe case of high-speed scanning and in the case of low-speed scanning,are shown to align for comparison. A difference of speed in the bothcases is caused by a multiplication factor of four in this example.According to the variable stage number shift register, the stage numberis switched by 0, that is, without delay. Generally, the delay of theelectronic circuit shows a substantially constant value without beingdependent on the scanning speed and therefore, according to the example,data stored to the image storing apparatus becomes effective from afifth pixel in the case of high-speed scanning and from a second pixelin the case of low-speed scanning.

[0020] When the delay is adjusted, adjustment can simply be carried outby correcting a position of an image provided in high-speed scanningwhile switching the stage number of the variable stage number shiftregister in the high-speed scanning to coincide with an image providedin low-speed scanning when the correction is 0. In this example, thedelay may be set to four stages (4 clocks).

[0021]FIG. 4 is a constitution example of the variable stage numbershift register defined by the invention. A plurality of D flip flop 26connecting outputs and inputs thereof are aligned in series and drivenby a reference clock 29. An output of the respective flip flop isconnected to respective tap of a stage number switching switch 27 andthe stage number can be selected. A signal provided to a signal input 28appears at a signal output 30 by being delayed by a period of thereference clock 29 multiplied by the stage number of selected ones ofthe D flip flop 26.

[0022] Although according to the embodiment, stage switching isrepresented by simple switches, an element such as a digital multiplexorcan naturally be used. Further, although according to the invention, thestorage start signal is delayed, the delay can similarly be realized bydelaying a signal such as the write signal.

[0023] The scanning type charged particle beam microscope according tothe invention is constructed by the constitution in which shift of ascanning image caused by a delay of an electronic circuit is correctedby delaying a timing of sampling a signal to a storing apparatus by anamount of delay of the electronic circuit by using a shift registerhaving a variable stage number and therefore, an effect described belowcan be achieved.

[0024] (1) The secondary electron information is stored to the storingapparatus after correcting the delay of the electronic circuit andtherefore, the scanning position and the storing position of a storingapparatus of the charged particle beam coincide with each other.

[0025] (2) The delay time can simply be corrected by observing an actualimage.

What is claimed is:
 1. A scanning type charged particle beam microscopewhich is a scanning type charged particle beam microscope using electronbeam, wherein when a scanned image is sampled to a storing apparatus insynchronism with a scanning signal, the scanned image is sampled aftercorrecting a shift of the scanned image caused by delay of an electroniccircuit by a shift register having a variable stage number.
 2. Thescanning type charged particle beam microscope according to claim 1,wherein the shift of the image caused by a difference in scanning speedis corrected while observing the scanned image by switching a stagenumber of the shift register having the variable stage number.